The present invention generally relates to down-the-hole drills (“DHD”). In particular, the present invention relates to a self-indexing down-the-hole drill.
Typical DHDs involve a combination of percussive and rotational movement of the drill bit to drill or chip away at rock. Such DHDs are powered by a rotatable drill string attached to a drilling platform, that supplies rotation and high pressure gases (e.g., air) for percussive drilling. Moreover, in percussive drilling, rock cutting is a result of percussive impact forces rather than shear forces. In other words, rotation of the DHD merely serves to rotationally index the drill bit to fresh rock formations after the drill bit impacts a rock surface rather then to impart shear cutting forces to the rock surface.
Conventional DHDs therefore, do not adequately address the needs of all industry drilling requirements. For example, in the exploration of oil and gas, directional drilling is often required. Directional drilling is the drilling of non-vertical boreholes or wells. Directional drilling requires that the DHD, along with its drill string, not rotate so that the required bend, or slant, can be developed with a bent sub. The bent sub allows a DHD to be angled to create the bend needed for the slanted borehole and is typically housed within the drill string. Therefore, as directional drilling requires a DHD capable of rotation for drilling, but also to not rotate such that a slanted borehole can be developed, directional drilling precludes the use of conventional DHDs.
Various attempts have been made to address the need for percussive directional drilling. For example, attempts have been made to partially overcome the problem by coupling a conventional down-the-hole motor with a conventional DHD. However, conventional down-the-hole motors typically do not operate at the necessary torque and speed for directional drilling. In addition, the long lengths of conventional down-the-hole motors and DHD assemblies renders such devices more susceptible to fatigue stresses and failure. Others have also attempted to induce rotation of DHD assemblies with integral rotation devices. However, such devices developed to date are unreliable and prone to failure due to the complexity and number of components required for such devices and because such devices are highly sensitive to abusive drilling environments.
Thus, there is still a need for a DHD hammer that overcomes the problems of length, motor deficiencies and reliability issues associated with conventional DHDs for use in directional drilling.